I. Field of the Invention
The present invention relates to medical sites through which fluid may be injected into or withdrawn from a patient without requiring use of sharp needles.
II. Description of Prior Art
In many medical situations, it is typical to provide a fluidfilled (e.g., saline) line coupled to a patient's circulatory system via a catheter inserted into the patient such as through the arm. A site is coupled in series with the fluid-filled line to provide access to the patient's circulatory system without further puncturing the patient such as with additional needles or catheters or the like. The site has a valve, such as a rubber septum or the like, through which access to the fluid line is by piercing through the septum with a needle, for example. When access is made, medications may be injected into the patient through the site and fluid line. Similarly, blood samples may be taken from the patient by withdrawal through the site. Examples of such uses are shown in U.S. Pat. Nos. 4,874,377; 5,148,811; 5,203,775; 5,221,271; and co-pending application Ser. No. 08/003,790, filed Jan. 13, 1993, the disclosures of all of which are hereby fully incorporated herein by reference.
As shown in those patents, it is possible to inject medicines into, or withdraw blood from, the patient through the site rather than by a further needle stick of the patient. But, as discussed in aforementioned U.S. Pat. No. 5,203,775, the use of sharp needles, even with sites, presents hazards to the medical personnel using the sites due the risk of needle sticks which could transmit disease.
The risk of needle sticks is greatly reduced when blunt cannulas, such as the distal plastic end of a typical syringe, can be used to access the fluid line through the valve of the site rather than a sharp needle. And while various proposals have been made to permit use of blunt cannulas, none have apparently met with much success for one reason or another.
One proposal for eliminating needles involves use of a slit septum as the site valve. The slit septum opens under pressure of a blunt cannula thereagainst to allow the blunt cannula to pass into and through the slit of the septum and into communication with the fluid line. While a slit septum has certain advantages in the drive to eliminate needles, it is not without a serious drawback. In particular, a slit across the septum tends to weaken the valve such that it may not be rigid enough to withstand back pressure from the fluid line when the cannula is removed. In such an event, the integrity of the valve is jeopardized which could result in fluid leakage from the valve with the attendant undesirable risks of infection and/or disease transmission.